Material isn't showing in viewport or render
I think you are doing this in eevee and for eevee you need to add Light probes for the reflections of the surrounding things so just press shift + a > Light probes > reflection cubemap 
add this on sphere and then go to indirect lighting menu in properties panel and bake the cubemap

and for more info on light probes just go to youtube and search for lightprobes and you will get tons of tutorials on it